The present invention relates to a method, to a device, and to the use of such a device for producing press-molded fuel made of moist biomass of all types, such as agricultural, forestry and horticultural products, including waste. Examples include grass clippings, nursery or kitchen waste, and waste from the industrial processing of biomass, for example in food processing, paper manufacturing or the like.
Such methods, and devices for carrying out the same, are known, for example, from WO 2004/067685 A1.
These methods comprise, for example, a drying process prior to the final press-molding process that serves to produce the press-molded fuel, a pressing process prior to the drying process so as to reduce the moisture content, and a first comminution process prior to the pressing process, whereby the efficiency of the subsequent pressing operation, which is to say the resulting reduction of the water content of the moist biomass, is increased.
The devices for carrying out these methods are constructed according to the requirements of these methods.
Compared to the conventional dry or largely dry biomass used as fuel, such as wood, or compared to biomass that may have been predried in the field, such as hay, moist biomass has a variety of advantages in terms of processing into fuel. On the one hand, moist biomass is available everywhere in large quantities, often without there being any other use therefor, so that otherwise it would have to be disposed of, for example composted, if it were not processed into fuel or would rot in the field without capturing the energy potential thereof.
Compared to predried biomass, biomass processed in the moist state has the advantage that losses of mass, such as those which occur, for example, due to seeds falling out with field drying, are avoided.
Above all, however, the combustion-related harmful substances, which are present in the biomass and which, like chlorine, for example, accelerate the corrosion of the combustion systems or negatively influence the ash behavior of the combustion material, remain in the biomass when it is dried naturally by evaporation and reduce the value thereof as a fuel. Primarily this disadvantage can be avoided to a significant extent if the moist biomass is compressed using known methods prior to the thermal drying process, so that the water contained therein is removed, along with a significant portion of the harmful substances.
Despite all the advantages thereof, the methods mentioned above, of course, also have disadvantages. Above all, they require large amounts of energy, meaning that they negatively impact the energy balance of the fuel to be produced. This is primarily due to the fact that compressing fresh biomass, such as grasses, which are commonly quite hard, requires considerable force and nonetheless results in insufficient moisture removal, so that the removal still leaves behind a significant moisture content in the material, which has already been compressed, thereby resulting in a particularly energy-consuming thermal drying process. This also means that combustion-related harmful ingredients in the biomass are only removed to a limited extent, because these substances are largely water-soluble and thermal drying does not, therefore, reduce them.
In addition, the considerable forces required for compressing the biomass are associated with major wear on the equipment, which is all the more significant because the biomass frequently contains impurities in the form of matter that increases abrasion, such as sand, inorganic waste and the like, particularly when grass clippings from agricultural or public traffic areas are involved.
This leads to the need for optimizing the known methods and the devices to be used therefor for producing fuels in the form of press-molded biomass made of moist starting material, so as to achieve better heating values and improved fuel properties from the fuel produced, with lower energy expenditure, notably in the thermal drying process, and with the lowest possible strain on the production facilities.